Feet, which are the human body's means for support and walking, have a complex structure capable of supporting the weight that bears on them both in static conditions and in dynamic conditions.
The complexity of this structure, dictated by the need to ensure the adaptability and flexibility required by a human being to stand upright, walk and run, requires a delicate balance, which if neglected can cause negative effects on the entire human body, such as for example excessive fatigue of the legs, lumbar pains, acquisition of an incorrect posture and/or gait, and many other muscular and spinal column disorders.
The shape of the sole of the foot is particularly important; due to its particular three-dimensional structure, by means of its anterior, lateral and posterior regions of the plantar surface, it constitutes the element for direct contact, also known as footprint, with the ground or with the insole of an item of footwear.
Accordingly, the footprint lacks the region related to the central surface, which due to the skeletal configuration of the anterior and posterior areas of the foot, which are supported by the action of the posterior tibial muscle, remains raised in an arc-like configuration, producing the so-called plantar arch.
The foot, as a whole, does not simply form a tripod, which would allow it to have exclusively static functions, but forms a three-dimensional architectural structure, comparable to a helix with a variable pitch, which is capable of coiling and uncoiling in accordance to the static and dynamic functions of the foot, accordingly affecting the plantar arch and therefore the shape of the footprint.
In order to ensure good functionality both in static conditions and during walking, said arch has a variable breadth.
While standing, said arch is in fact flattened in order to allow stable support, whereas while walking there is an alternation of contraction and distension of said arch, so as to achieve an effective dynamic balance.
The contraction or lifting of said arch and its distension are achieved respectively by means of the outward rotations, also known as supinations, and inward rotations, also known as pronations, of the calcaneum with respect to the tibia.
To allow this movement of the foot to yield the required results and therefore ensure the support of the human body without causing aches or fatigue thereof, the maximum and minimum breadths of the arch of the foot must be contained within very specific limits, which determine the morphological normality of the foot.
An excessive distension of the arch of the foot or an excessive contraction thereof may lead, moreover, to fatigue of the posterior tibial muscle, which is thus forced to contract excessively, transmitting a feeling of discomfort.
In order to improve the contact of the sole of the foot, plantar inserts are currently used which can be rendered more or less anatomically contoured by adding supports at the concave regions of the sole of said foot, said supports being suitable to lift passively the plantar arch, or by means of footwear correction devices, by assembling together with the plantar insert supports capable of redistributing in a targeted and case-specific manner the loads on specific points of the sole of the foot.
The main drawback of these known types of plantar insert is that the foot is prevented from performing certain natural and physiological movements, causing fatigue and discomfort.
Another drawback of known types of plantar insert relates to the fact that in most cases they are made to measure, requiring high production costs and the use of specialized labor.
Italian utility model No. 233568 is also known which discloses a regenerating anatomically-contoured plantar insert, in which the upper surface has a steep downward inclination in the outer region of the foot.
This regenerating anatomically-contoured plantar insert therefore induces an increased supination of the foot and therefore a lifting of the plantar arch of the foot, which is achieved without requiring the presence of protrusions that directly support said region of the sole of the foot.
However, even this solution does not solve all the drawbacks noted earlier.